The baked potato was returned stone cold. Our manager Scott had scolded Nigel the chef, the fuming Nigel had thrown the potato into the bin, but once Nigel was gone, Renata had retrieved the potato and perched it above the carousel in the dishwash. She had dabbed blobs of mayonnaise on to the potato and, from the litter of uneaten food washing down the waste disposal, she had taken two little raisins from the spotted dick for eyes and some celery for fangs. Once his face was arranged, Jack Potato glared down at us with an expression of terrible black savagery.

Our setting, incidentally, is the hospital canteen where the agency typically posts Renata and I for the afternoon shift. Over the following days, Jack Potato had dried into a glaring mad husk, the size of a coconut’s baby, but nobody had bothered to throw him away, or else they were afraid that this would be taking some sort of liberty with Renata’s property. And over the following weeks, Jack Potato had assumed an indispensable role in the psychoanalysis which I practised at the canteen.

The canteen is always very busy, it is a demanding working environment, and our customers often exacerbate the situation with their stupid questions and idiotic remarks. Yet however brainless the customer’s contribution, one must always remain stoical. Like the statue of a Victorian soldier in a town square which is daily showered with pigeon droppings, one must generate an impression of command, grandeur, and heroic aloofness from the circumstances which conspire against such ideals. Once in the privacy of the kitchen, however, one’s emotions could run riot:

“Renata,” I would instruct. “Fetch Jack Potato.”

Jack Potato was taken down from his perch.

“Renata,” I continued. “I want Jack Potato to say, “Do you have any Soya milk? Only I’m a vegan and I can’t drink any milk that is unethical.””

“Is this in a man’s or a woman’s voice?” Renata asked.

“A woman’s, obviously.”

“Young or old?”

“About middle aged.”

“And accent?”

“Scottish, but I can’t be more specific. Possibly Glasgow.”

Renata held Jack Potato by the fingertips and bobbed him lightly up and down as she produced the required voice. “Do you have any Soya milk? Only I’m a vegan and I can’t drink any milk that is unethical.”

I stared Jack Potato in the eye and began to scream, with such devastating force that my whole being shot to the back of my mind and my body seemed weightless and soaring like that of a pouncing cat. “You stupid bastard!” I bellowed. “You stupid fucking retard! Milk! I’ve never heard anything like it! You want me to find some fluid drained from Soya beans and pretend that it is milk? You think that milk from a cow is “unethical”? You don’t care about ethics at all – you just want to be awkward and fucking annoy me! People like you would drink your own piss if you thought that it would make you different from everybody else! You stupid, stupid bastard!”

As the weeks passed, Jack Potato came to take the role of various awkward customers in my therapy sessions. One had an imaginary medical condition which rendered eating a peanut the equivalent of stepping on a landmine, another was wary of cucumbers because certain types of them were grown in some African valley where they castrated homosexuals (“could you please check?”), whilst a third needed to have entire meals pulped into a slurry and then slurped through a straw to appease the tyrannies of their digestion. There was one woman who complained that after enjoying an apparently innocuous cup of tea at our canteen, she had for the next ten weeks suffered from extreme diarrhea eight times a day. Henceforth, she always arrived at the canteen with a little chemistry set and she subjected every cup of tea to various elaborate experiments before she would hand over the ninety pence.

On each occasion, I would smile at the customer, whilst in the kitchen Jack Potato would face my fury at their stupidity. Now I am not going to start demanding that you accept some incontrovertible spiritualist truth – I do not care whether you believe me or not – and, to be honest, I am uninterested in reconciling the following facts to any sort of sense. These events simply happened and there is no sensible explanation for them. But what remains indisputable is that Jack Potato had repeatedly absorbed a terrible negative energy, and that this had somehow invested him with qualities which are not apparent in other potatoes.

Whilst Jack Potato was soaking up my negativity, there was a great drama unfolding at the hospital, which the local media covered daily and which was briefly the lead story in national news bulletins. A newborn baby was discovered to have a complicated heart defect and she required immediate surgery. The surgeons battled for three days to keep the infant alive, whilst a small crowd of people with nothing better to do gathered outside the hospital beneath banners of support. Unfortunately the baby eventually succumbed to her condition and she died. On the afternoon following her death, her haggard and demoralised parents appeared at our canteen for the final time. They were met with an approving round of applause from the other diners. Touchingly, the mother was still bearing the carrycot in which her daughter should have left the hospital.

I had decided not to charge the parents for their tea as an expression of sympathy, but Nigel warned me that this was not company policy and I got so confused with the till that I accidentally charged them double.

The parents went to sit in the canteen and moments later there was a bloodcurdling roar. Everybody was running to help the stricken mother, a doctor sat her down and took her pulse, one nurse shooed away the gawping onlookers whilst another went to fetch a glass of water, the father was weeping to himself, and all the while the mother was jabbering about something which she had apparently seen in the carrycot:

“Oh help me, it was horrible… It was really horrible!… It had a nasty little face with evil wicked little eyes… and it had nasty biting teeth… and… oh help me… it looked like a potato!”

Renata and I exchanged a significant glance.

Back in the kitchen, we looked to the spot over the carousel where Jack Potato usually sat. He was gone.

“What’s all that clattering in the ventilation?” the manager Scott asked. “It sounds like there’s some sort of animal in there.”

Over the afternoon, the canteen experienced acute malfunctions with the air conditioning. At first, the customers were assailed with ice cold air, there were dozens of complaints, and several people left. Next, there was an almighty heat wave, the canteen became as sweltering as a furnace, and the diners who had previously sat shivering under layers of coats were now stripping down to their vests.

“This is Jack Potato’s work!” I swore. A strange image had popped into my head of the potato whistling and giving an eager thumb’s up as he surveyed a room full of fat old ladies undressing.

“It’s the air conditioning!” Renata raged triumphantly, as if the latest antics of this entity had finally affirmed all of her suspicions about it. At the canteen the controversy over the air conditioning would last for eternity: whatever setting it was on was too hot or too cold, and it never failed to torture Renata. She had complained to her union six times.

There was a succession of loud bumps from the ventilation. “It’s definitely that potato!” I said.

“I don’t know where he is,” Renata admitted. “I checked with Nigel and he hasn’t been served to any of the customers.”

“We could get him out with a ferret,” I was muttering to myself.

“Do we have a ferret… in the utensils drawer?”

“Don’t get smart with me!” I exploded.

Scott made a solemn appearance at the kitchen door. “We’re going to have to close the canteen” he told us, now responsible-Scott rather than silly-Scott. “This is a hospital, there are lots of sick people here, lots of old people, and their health is being put at risk.”

Scott gave the evacuation order over the Tannoy system, the grumbling customers put down their knives and forks and they collected their coats, but when they got to the sliding doors they were jammed shut.

Scott came out of his office to try and convince everybody that the situation was under control, although some of the customers were now panicking in the heat. “Smash the doors? Crowbar them open?” I offered.

Scott shook his head. “That would give the wrong impression.”

There was suddenly a shriek. A woman was backing against the wall, her eyes huge. “There’s an animal in here! I saw it run around the back of the vending machine!”

We all peered into the darkness. Amongst the tangle of wires, furred with dust, I could make out something watching us, a shapeless presence. Then there was a hasty clattering – the thing had shot out the other side of the vending machine. As quick as a rifle shot, I had grabbed a woman’s coat and thrown it over the animal and then I had a chair flailing over my head and I brought it down crash on top of the coat. I had brought it down again and again and again before Scott seized my arm.

The woman was outraged. “My coat! It’s totally ruined!”

“There’s nothing under there!” Renata hissed at me furiously.

“I’m truly sorry,” Scott said to the woman. “I can see that it’s a very expensive coat…”

“What is it with you and this potato?” Renata demanded. “I’ve never seen you so angry in all the time that I’ve known you.”

In truth, the potato seemed to personify all of the awkward customers and idiotic questions that I had ever had to deal with. I wanted to annihilate it.

The heat was now so great that several of the diners had blacked out and many of them were extremely distressed. My frantic attempts to prize open the doors were getting nowhere and they had only left me reeling in the heat. Renata suddenly had a plan and such was the urgency of the situation that Scott could only agree to it. If some of the customers could be lifted up into the ventilation overhead, they could crawl along until they were over the corridor outside the canteen, whereupon they could drop down to safety. The drawback to this was that they would have to endure some seriously intense heat whilst they were inside the ventilation.

Speed was of the essence. Scott started to yell orders at the customers and they were so impressed that they just did what they were told. The customers who were suffering the most in the heat were sent first and we had lifted over a dozen of them up into the ventilation before the proceedings ground to a halt. It seemed that there was a blockage in the ventilation – the first customer in the queue had passed out and the others could not push past her. Renata climbed up to try and help, but she soon retreated from the customers’ hideous cries and screams – the hot metal lining of the shaft was scorching their skin. These customers would spend several hours trapped inside the ventilation and their torments are beyond description.

Meanwhile, down in the canteen Jack Potato’s reign of terror was only just beginning. The microwave in the kitchen burst into flames, sending a gigantic fireball sweeping through the canteen. It transpired that some special ingredients had been added to the Soup of the Day – possibly the detergent from the industrial dishwasher – and before long the customers who had dined on this were vomiting their insides out. In the toilets, the sinks had been blocked with toilet paper and the taps were flowing merrily, so that the water was soon around our ankles, followed by hundreds of volts from various stray wires. How does one negotiate a surrender with a rampaging potato? In any event, it was soon every man for himself – Renata and I broke out of the kitchen window, hauling Scott’s electrocuted carcass after us. When the fire brigade arrived they managed to force open the doors and help the survivors to safety, although retrieving those trapped inside the ventilation required a lengthy and protracted surgery.

Jack Potato still remains in the ventilation or down in the sewers – perhaps he has been crowned king of the underworld – perhaps he now sits on his throne scheming away with a court of rats scampering at his every whim.